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Author Topic: My 'Witches' Brew for Zinc plating removal.  (Read 1812 times)
ashimotok0
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« on: April 15, 2015, 01:59:38 AM »

Got loads of spokes to re-plate and was concerned about hydrogen embrittlement using strong acids to remove the old zinc plate so have this  'witches'  brew to try, instead :-

Sorry about UK sources but I am sure you can buy in the USA /Australia etc,

To make up 1 litre of stripping solution:-

100 grammes ---  Sodium Hydroxide  (Source B &Q, Wilkinsons, ect)

90 grammes --- EDTA---- (EthyleneDiamineTetraAcetic acid)  Source:   http://www.ebay.co.uk/itm/130544728488?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

4 grammes ----  Triethanolamine --- Source :    http://www.ebay.co.uk/itm/321368003934?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Immersion is at 70 degrees C +/- 5 degrees.

Will let you know how I get on.

Ash
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Wayne
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« Reply #1 on: April 15, 2015, 08:59:58 AM »

Is CLR considered a "strong acid" Ash? I have used it and the zinc just fizzes off overnight.
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patriotcommercial
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« Reply #2 on: April 15, 2015, 08:29:49 PM »

I think evaporust Removes the plating
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Honda CB750 Sandcast Forum
« Reply #2 on: April 15, 2015, 08:29:49 PM »

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ashimotok0
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« Reply #3 on: April 16, 2015, 06:29:51 AM »

I once worked for a company in the 1980's who cadmium  plated mechanical fasteners for conveyor belting but they changed to BZP because of the toxicity of the cyanide used, and  so they changed to BZP instead. I was told by them  that strong acid removal of zinc plating from steel  can cause hydrogen embrittlement and the formula quoted was used to remove the zinc on test samples to determine the amount of zinc deposited, without causing hydrogen embrittlement. I plan to use it on spokes, just to be on the safe side, because these are a safety critical components. From what I understand you also need to bake the spokes in an oven after plating.

Mr Honda would have known ..he was a metallurgist!

Ash.

« Last Edit: April 16, 2015, 06:33:20 AM by ashimotok0 » Logged
hondasan
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« Reply #4 on: April 16, 2015, 03:08:27 PM »

Electroplating, which bzp tends to be, does potentially cause hydrogen embrittlement. A de-embrittlement treatment is advised ESPECIALLY for components which are subsequently stressed in tension - bolts, spring washers, spokes. The higher the strength of the  material, the greater the risk of H.E. And of course bolts etc tend to be made of higher strength grades of steel to enable higher fastening loads.
Springs especially (design / testing of the last 35 years) should be de-embritled. Silicon chrome based grades of steel should NEVER be bzp'd.

Cheers - Chris
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Chris R.
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ashimotok0
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« Reply #5 on: May 14, 2015, 04:51:39 PM »

Well just got the EDTA in a 500g lot after waiting ages for the eBay supplier to deliver . Running at 70 degrees C it strips the zinc plating fairly quickly and beautifully.. good result and fairly inexpensive. Probably about 5.5 GBP for 2.5 litres of the 'brew'.
This is from a British Coal Board spec. for removing the plating on the steel fasteners used for holding together large conveyor belts without causing hydrogen embrittlement.

Ash
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toycollector10
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« Reply #6 on: July 06, 2015, 12:39:01 AM »

I use brick cleaner, or suphuric acid, to clean up the bolts then polish them prior to submitting for replating. That's what the guys over on the Z1 forum do. Just dip for a second or two then rinse under running water and dunk them in a bucket of water overnight. I suppose I've done it all wrong?
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